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Fluid quality sensor

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20120286810 patent thumbnailZoom

Fluid quality sensor


An object of the present invention is to accurately detect concentrations of mixtures in a fluid. An internal electrode 23 is disposed on the inner side of an external electrode 22 coaxially with the external electrode 22, and a plurality of points in the length direction of the internal electrode 23 are supported by a casing 21 via supporting members 28a and 28b. The state of a fluid S passing through a passage 26 between the external electrode 22 and the internal electrode 23 is detected based on electrostatic capacitance between the external electrode 22 and the internal electrode 23.

Browse recent Panasonic Corporation patents - Osaka, JP
Inventors: Takashi TSURUTA, Kazuhiro NISHIKAWA, Koichi KUBOTA, Takuto SHIBAYAMA
USPTO Applicaton #: #20120286810 - Class: 324663 (USPTO) - 11/15/12 - Class 324 


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The Patent Description & Claims data below is from USPTO Patent Application 20120286810, Fluid quality sensor.

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FIELD OF THE INVENTION

The present invention relates to a fluid quality sensor for detecting the concentration of a fluid by a capacitive sensing method.

BACKGROUND OF THE INVENTION

FIG. 11 shows a fluid quality sensor of WO2007/019577. In order that a fluid S flowing from an upstream fluid pipe 25 toward a downstream fluid pipe 27 may be detected based on electrostatic capacitance and temperature, a pipe 61 connected to the fluid pipe 25, a pipe 62 connected to the fluid pipe 27, and an intermediate pipe 63 interposed between the pipes 61 and 62 form a fluid path 64. An internal electrode 65 is disposed on the fluid path 64 inside the immediate pipe 63 via a supporting member 66. The intermediate pipe 63 is an external electrode, and the internal electrode 65 is electrically insulated from the immediate pipe 63 by the supporting member 66. A temperature sensor 67 indirectly detects the temperature of the internal electrode 65 with a detector 68 thermally connected to the supporting member 66.

Thus, based on a capacitance value between the intermediate pipe 63 and the internal electrode 65 and a temperature detected by the temperature sensor 67, the state such as the concentration of the fluid is detected.

Further, FIG. 12 shows a fluid quality sensor of Japanese Patent No. 2639753.

Pipes 70 and 71 are joined to each other in a substantially T-shape. A fluid S flows in from an inlet 70a on one end of the pipe 70 and flows out from an outlet 71a on one end of the pipe 71. The other end of the pipe 70 is closed by an electrode inserting member 72. An internal electrode 73 is inserted from the other end toward the one end of the pipe 70. Reference numeral 74 denotes a temperature sensor attached to the outer peripheral surface of the pipe 70.

Thus, based on a capacitance value between the pipe 70 and the internal electrode 73 and a temperature detected by the temperature sensor 74, the state such as the concentration of the fluid S is detected.

DISCLOSURE OF THE INVENTION

However, in the first related art example of FIG. 11, the rod-shaped internal electrode 65 in the fluid path 64 is held at only one point by the supporting member 66, and thus excessive stress is applied on the supporting member 66 according to the flow rate and the viscosity of the fluid S. It is highly likely that the excessive stress applied on the supporting member 66 causes the internal electrode 65 to vibrate or be displaced. In order to avoid the problem, in general, the thickness of the supporting member 66 or a distance between electrodes is increased. However, the increased distance between electrodes inevitably reduces the detection accuracy. Further, the cross-sectional area of the fluid path becomes non-uniform and the flow of the fluid S is disturbed, and thus the detection accuracy becomes unstable in sensing the fluid S with time and small changes in the properties of the fluid S are hardly noticed.

The present invention has been devised to solve the problem. An object of the present invention is to provide a fluid quality sensor capable of detecting the fluid S with high accuracy over a long time despite the flow rate and the viscosity of the fluid S.

A fluid quality sensor for measuring mixture fluid includes: a tubular external electrode disposed on a first passage on an inner side of a tubular casing; an internal electrode having supporting members at both end connected to the casing so as to be disposed on an inner side of the external electrode coaxially with the external electrode, a intake part which are attached to one end of the casing, and have a second passage communicated with the first passage formed between an inner circumference of the external electrode and an outer periphery of the internal electrode; and a outlet part which are attached to another end of the casing, and have a third passage communicated with the first passage, wherein concentration of a fluid passing through the first passage is detected based on electrostatic capacitance between the external electrode and the internal electrode.

Preferably, both ends of the internal electrode are extended along the second and third passages respectively, and cross-sectional areas of the second passage and the third passage are equal to that of the first passage.

Preferably, the both ends of the internal electrode are cone-shaped, and the second and third passages of the intake and outlet parts are tapered along the cone-shapes of the both ends of the internal electrode respectively. Angles of the cone-shapes of the both ends of the internal electrode are 10° to 60°.

Preferably, at least two points in a outer surface of the internal electrode are attached to the casing by the supporting members.

Preferably, first members are attached to both ends of the external electrode, the first members having holes in centers of the first members through which the internal electrode passes and being made of electrical insulators, second members are attached onto outer sides of the first members, the second members having holes in centers of the second members through which the internal electrode passes and being made of electrical conductors, and inner surfaces of the second members and an outer surface of the internal electrode are connected by the supporting members, the first members with the external electrode attached thereto and the second members with the internal electrode attached thereto are inserted into the first passage, and are positioned in a diameter direction of the casing, the intake and outlet parts are attached to the both ends of the casing respectively, so that the external electrode, the internal electrode, the first members, and the second members are located, and the external electrode and the first members, the first members and the second members, and the second members and the adapters are sealed with sealing materials. A temperature sensor is connected to the external electrode.

According to the present invention, the plurality of points of the internal electrode in the direction of the passage are supported by the casing via the supporting members such that the internal electrode is held on the inner side of the external electrode coaxially with the external electrode. Thus, the position of the internal electrode can be precisely retained and high detection accuracy can be secured over a long time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a fluid quality sensor according to a first embodiment of the present invention;

FIG. 2 is a fabrication process drawing according to the first embodiment;

FIG. 3 is an enlarged cross-sectional view showing the main part of FIG. 2;

FIG. 4 is a cross-sectional view taken along the arrows A-A of FIG. 1;

FIG. 5 is a cross-sectional view taken along the arrows B-B of FIG. 1;

FIG. 6 is a configuration diagram showing urethane foaming equipment in a first example;

FIG. 7 is an input/output characteristic diagram of measurement results of electrostatic capacitance in the first example;

FIG. 8 is a configuration diagram showing urethane foaming equipment in a second example;

FIG. 9 is an input/output characteristic diagram of measurement results of electrostatic capacitance in the second example;

FIG. 10 is an enlarged cross-sectional view showing a main part according to a second embodiment of the present invention;

FIG. 11 is a cross-sectional view of a fluid quality sensor of the related art described in WO2007/019577; and

FIG. 12 is a cross-sectional view showing a fluid quality sensor of the related art described in Japanese Patent No. 2639753.

DESCRIPTION OF THE EMBODIMENTS

The following will describe embodiments of the present invention in accordance with FIGS. 1 to 10.

First Embodiment

FIGS. 1 to 5 show a fluid quality sensor 20 according to a first embodiment.

The fluid quality sensor 20 includes: a tubular casing 21; a tubular external electrode 22 fixed to the inner side of the casing 21; an internal electrode 23 disposed on the inner side of the external electrode 22 coaxially with the external electrode 22; and adapters 24a and 24b attached to ends of the casing 21. A fluid S flows into the fluid quality sensor 20 from a fluid pipe 25 connected to the adapter 24a.

The fluid S having flowed into the fluid quality sensor 20 passes through a detection passage 26 formed between the inner circumference of the external electrode 22 and the outer periphery of the internal electrode 23 and flows out of a fluid pipe 27 connected to the adapter 24b via the adapter 24b.

The internal electrode 23 having two cone-shaped ends is supported by the casing 21 via supporting members 28a and 28b at multiple points, in this embodiment, at two points in the direction of the detection passage 26. The internal electrode 23 is larger in length than the external electrode 22, and the supporting members 28a and 28b are positioned outside the opposed part of the external electrode 22 and the internal electrode 23.

The configuration will be specifically described based on a fabrication process.

As shown in FIG. 2(a), first members 30a and 30b, which have holes 29 in the centers thereof and are made of electrical insulators, are attached to two ends of the external electrode 22.

Onto the outer sides of the first members 30a and 30b, second members 32a and 32b are attached which have holes 31 in the centers thereof and are made of electric conductors, and the inner circumferential surfaces of the second members 32a and 32b and the outer peripheral surface of the internal electrode 23 are connected by the supporting members 28a and 28b which are made of electric conductors.

The inner circumference of the external electrode 22, the first member 30a, the second member 32a, and an internal passage E of the adapter 24a are flush with each other. Further, the inner circumference of the external electrode 22, the first member 30b, the second member 32b, and an internal passage E of the adapter 24b are flush with each other.

Specifically, as shown in FIG. 3, a bolt 35 is inserted into a through hole 33 formed in the second member 32a and a center hole 34 of the supporting member 28a, and the tip of the bolt 35 is screwed and tightened into the internal electrode 23. Bolting is performed also on the side of the second member 32b.

A contact surface between the cuter periphery of the end of the external electrode 22 and the inner circumferential surface of the first member 30a is sealed with an O-ring 36. A contact surface between the first member 30a and the second member 32a is sealed with an O-ring 37. A contact surface between the outer periphery of the end of the external electrode 22 and the inner circumferential surface of the first member 30b is sealed with an O-ring 38. A contact surface between the first member 30b and the second member 32b is sealed with an O-ring 39.

Next, as shown in FIG. 2(b), the first members 30a and 30b with the external electrode 22 and the second members 32a and 32h with the internal electrode 23 are inserted into the passage on the inner side of the casing 21, and are positioned in the diameter direction of the passage on the inner side of the casing 21. The outer peripheral surface of the first member 30a and the inner circumferential surface of the casing 21 are sealed with an O-ring 40, and the outer peripheral surface of the first member 30b and the inner circumferential surface of the casing 21 are sealed with an O-ring 41.

In FIG. 2(c), the adapters 24a and 24b are attached to the ends of the casing 21 with bolts 42. A contact surface between the second member 32a and the adapter 24a is sealed with an O-ring 43, and a contact surface between the second member 32b and the adapter 24b is sealed with an O-ring 44. The internal passages E of the adapters 24a and 24b are tapered along the cone-shaped ends of the internal electrode 23.

After the above-described fabrication process, a temperature sensor 46 is thermally connected to the outer peripheral surface of the external electrode 22 exposed from a hole 45 of the casing 21. As shown in FIG. 1, a cylinder 47 is attached to the outer peripheral surface of the casing 21 so as to be communicated with the hole 45.

FIG. 4 is a partial cross-sectional view taken along the arrows A-A of FIG. 1. FIG. 5 is a partial cross-sectional view taken along the arrows B-B of FIG. 1.

In this configuration, a capacitance value between the external electrode 22 and the internal electrode 23 is measured to determine the chemical concentration of the fluid S. At this point, the dielectric constant varies depending on the temperature of the fluid S in addition to the concentration. Thus, the temperature sensor 64 is provided. For the measurement of the capacitance value between the external electrode 22 and the internal electrode 23 and the temperature sensor 46, a known technique is used to implement the measurement.

The two ends of the internal electrode 23 are cone-shaped and the inner circumferential surfaces of the adapters 24a and 24b are tapered along the ends of the internal electrode 23 such that the cross-sectional areas of flow paths between the internal electrode 23 and the adapter 24a and between the internal electrode 23 and the adapter 24b are substantially equal to the cross-sectional area of a flow path between the internal electrode 23 and the external electrode 22 except for the locations of the supporting members 28a and 28b, in the cross-sectional area of a flow path from the fluid pipe 25 through the fluid quality sensor 20 out of the fluid pipe 27. Thus, the flow of the fluid S can be made a laminar flow passing through the detection passage 26.

When the maximum angle of the cone-shaped portion of the internal electrode 23 exceeds 60°, the resistance of the fluid increases and a force acts on the sensor, thereby impeding stable measurement. When the minimum angle thereof is smaller than 10°, the sensor is reduced in thickness, and is thus distorted or bent, thereby preventing measurement. Consequently, the angle of the cone-shaped portion is preferably within a range of 10° to 60°. Further, when the maximum angle is reduced from 60° to 45°, the resistance of the fluid decreases, most of the fluid to be detected becomes a laminar flow, the measurement is stabilized, and the measurement accuracy is increased. When the minimum angle is increased from 10° to 20°, the rigidity of the sensor increases, the cone-shaped portion becomes smaller in length in the axial direction, and the total length of the sensor is reduced, so that the measurement accuracy is increased. Consequently, the angle of the cone-shaped portion is more preferably within a range of 20° to 45°.

In the drawings, the angles of the cone-shaped portions of the internal electrode 23 are set at 25° such that the cross-sectional area of the detection passage 26 becomes constant.

If the cone shape on the downstream end of the internal electrode 23 is eliminated, the fluid swirls in the vicinity of the downstream side of the internal electrode 23, and the flow therearound is disturbed. As shown in FIG. 1, when the detection passage 26 of the fluid quality sensor 20 is straight, the two ends of the internal electrode 23 are preferably cone-shaped.



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stats Patent Info
Application #
US 20120286810 A1
Publish Date
11/15/2012
Document #
File Date
08/20/2014
USPTO Class
Other USPTO Classes
International Class
Drawings



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